Fatty acid amide hydrolase (FAAH) is known to hydrolyze endocannabinoid to inactivate it (Non-Patent Document 1). Endocannabinoid is a generic term for biomolecules that act on cannabinoid receptors to exhibit their physiological activities. As typical endocannabinoids, anandamide, palmitoylethanolamide, oleamide, and 2-arachidonoylglycerol are known. Furthermore, Δ9-tetrahydrocannabinol which is considered as an active ingredient of Cannabis (marijuana) is known to activate a cannabinoid receptor (Non-Patent Document 2).
In mammals, two types of cannabinoid receptors, CB1 and CB2, have heretofore been known. CB1 is expressed in the central and peripheral nervous systems, and when activated, it exhibits a psychological action, an analgesic action, or the like. CB2 is expressed in the immune system, and when activated, it exhibits an anti-inflammatory action, an analgesic (inflammatory) action, or the like.
Nonsteroidal anti-inflammatory drugs, and narcotic analgesic drugs such as morphine and the like, that are ordinary analgesics, are known to be weakly effective for neuropathic pain. In the medical field, antiepileptic drugs such as pregabalin and the like, and antidepressant drugs such as duloxetine and the like are used for pain relief, but their analgesic effects are insufficient, and there are problems with central side effects such as sleepiness, dizziness, and the like.
A cannabinoid receptor agonist exhibits effectiveness for patients with neuropathic pain, but its use is greatly limited due to its psychological action (Non-Patent Document 3).
On the other hand, when an FAAH inhibitor is administered to an animal, it exhibits an analgesic effect against neuropathic pain and inflammatory pain, but side effects observed when a cannabinoid receptor agonist is administered to an animal, such as sedation, decreased body temperature, catalepsy, and the like, are not observed (Non-Patent Documents 4 and 5), and thus an FAAH inhibitor is expected to be an excellent pharmaceutical for treating pain, in particular, a pharmaceutical for treating neuropathic pain.
As compounds having an FAAH inhibitory activity, compounds which are capable of acting as an analgesic, an antianxiety drug, an antiepileptic drug, an antidepressant, an antiemetic, a cardiovascular agent, or an antiglaucomatous agent, are known.
For example, Patent Document 1 discloses the compound represented by the following formula (A), as a compound having an FAAH inhibitory activity.

(In the formula, B represents a variety of ring groups which may be substituted, or the like, and A represents phenyl which may be substituted, phenylalkyl which may be substituted, dibenzofuranyl, dibenzothienyl, naphthoyl, indolyl, fluorenyl, or carbazolyl. For the details, refer to this publication).
Furthermore, Patent Document 2 discloses the compound represented by the following formula (B) as a compound having an FAAH inhibitory activity.

(In the formula, R represents a variety of ring groups which may be substituted, or the like, and X and Q are the same as or different from each other and represent O or S, respectively. Further, R1 and R2 may be combined with an N atom to which they optionally bind to form a substituted or unsubstituted ring. For the details, refer to this publication).
Furthermore, Patent Document 3 discloses the compound represented by the following formula (C) as a compound having an FAAH inhibitory activity.

(For the details, refer to this publication).
All of the compounds disclosed in this document have different structures from the compound of the formula (I) of the present invention.
Furthermore, Patent Documents 4 and 5 disclose the urea compound represented by the following formula (D) as an FAAH inhibitor.

(In the formula, Z represents O or S, and R2 represent piperidine-1,4-diyl or piperazine-1,4-diyl, each of which may be substituted. For the details, refer to these publications).